Pump system having open-loop torque control

ABSTRACT

A pump system is disclosed. The pump system may have a pump with a displacement that is variable, and an actuator movable to adjust the displacement of the pump. The pump system may also have an electro-hydraulic valve fluidly connected to the actuator and configured to control movement of the actuator, and a variable resistor mechanically connected to at least one of the actuator and the pump. The variable resistor may be adjustable by movement of the at least one of the actuator and the pump to vary a current passing through the electro-hydraulic valve.

TECHNICAL FIELD

The present disclosure relates generally to a pump system, and moreparticularly, to a pump system having open-loop torque control.

BACKGROUND

Hydraulic tool systems typically employ multiple actuators provided withhigh-pressure fluid from a common pump. In order to efficientlyaccommodate the different flow and/or pressure requirements of theindividual actuators, the pump of these systems generally has a variabledisplacement. That is, based on the individual and/or combined flow andpressure requirements of the actuators, the displacement of the pumpchanges to meet demands of the actuators while remaining within torqueabsorption limitations placed on the pump by an associated engine.

Generally, one or both of the pump's displacement and discharge pressureare measured by different sensors, and an associated controllerresponsively commands a corresponding displacement change to managetorque absorption. An exemplary pump of this type is described in U.S.Pat. No. 5,515,829 that issued to Wear et al. on May 14, 1996 (“the '829patent”).

Although the pump described above may be adequate for many applications,it may also require valuable computing time from the controller andmultiple feedback loops to properly maintain a desired torque absorptionas displacement and pressure change. The multiple feedback loops canaffect a responsiveness of the pump and possibly cause pump and/orengine instabilities. In addition, the sensors utilized for control ofthe pump may add unnecessary cost and complexity to the system.

The disclosed pump system is directed to overcoming one or more of theproblems set forth above and/or other problems of the prior art.

SUMMARY

In one aspect, the present disclosure is directed to a pump system. Thepump system may include a pump with a displacement that is variable, andan actuator movable to adjust the displacement of the pump. The pumpsystem may also include an electro-hydraulic valve fluidly connected tothe actuator and configured to control movement of the actuator, and avariable resistor mechanically connected to at least one of the actuatorand the pump. The variable resistor may be adjustable by movement of theat least one of the actuator and the pump to vary a current passingthrough the electro-hydraulic valve.

In another aspect, the present disclosure is directed to method ofcontrolling a pump. The method may include operating the pump topressurize a fluid, and generating an electronic signal indicative of acommand to adjust a displacement of the pump. The method may alsoinclude hydro-mechanically adjusting the displacement of the pump basedon the signal. Hydro-mechanically adjusting the displacement the pumpalso simultaneously modifies a resistance of the signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial illustration of an exemplary disclosed machine;

FIG. 2 is a schematic illustration of an exemplary disclosed pump systemthat may be utilized in conjunction with the machine of FIG. 1; and

FIG. 3 is a schematic illustration of another exemplary disclosed pumpsystem that may be used in conjunction with the machine of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary machine 10 performing a particularfunction at a worksite 12. Machine 10 may embody a stationary or mobilemachine, with the particular function being associated with an industrysuch as mining, construction, farming, transportation, power generation,oil and gas, or another industry known in the art. For example, machine10 may be an earth moving machine such as the excavator depicted in FIG.1, in which the particular function includes the removal of earthenmaterial from worksite 12 that alters the geography of worksite 12 to adesired form. Machine 10 may alternatively embody a different earthmoving machine such as a motor grader or a wheel loader, or a non-earthmoving machine such as a passenger vehicle, a stationary generator set,or a pumping mechanism.

Machine 10 may be equipped with multiple systems that facilitateoperation thereof at worksite 12, for example a tool system 14, a drivesystem 16, and an engine system 18 that provides power to tool system 14and drive system 16. During the performance of most tasks, power fromengine system 18 may be split between tool system 14 and drive system16. That is, during machine travel between excavation sites, amechanical output of engine system 18 may be converted to a rotation oftraction devices that propel machine 10, in some examples by way of ahydraulic or hydro-mechanical transmission (not shown). When parked atan excavation site and actively moving material, the mechanical outputof engine system 18 may be converted to hydraulic power supplied to oneor more working actuators of tool system 14.

As illustrated in FIG. 2, engine system 18 may include a heat engine 20,for example an internal combustion engine, that is coupled with a pumpsystem 24. Pump system 24 may include a collection of components thatare driven by engine 20 to hydraulically power tool and/or drive systems14,16. Specifically, pump system 24 may include a low-pressure tank 26,and a pump 28 fluidly connected to tank 26 by way of an inlet passage 30and to systems 14, 16 by way of an outlet passage 32. Pump 28 may bedriven by engine 20 to draw in low-pressure fluid from tank 26 anddischarge the fluid at an elevated pressure to systems 14, 16. Pumpsystem 24 may also include a displacement actuator 34 associated withpump 28 and movable to vary a displacement of pump 28, a displacementcontrol valve 36 operable to cause movement of displacement actuator 34,and a controller 38 configured to regulate operation of displacementcontrol valve 36.

Pump 28 may be a swashplate-type pump and include multiple piston bores(not shown), and pistons (not shown) held against a tiltable swashplate40. One piston may be slidably disposed within each of the bores andbiased into engagement with a driving surface (not shown) of swashplate40. The pistons may reciprocate within the piston bores to produce apumping action as swashplate 40 rotates relative to the pistons(swashplate 40 may rotate while the pistons and associated bores remainstationary, or the pistons and bores may collectively rotate whileswashplate 40 remains stationary). Swashplate 40 may be selectivelytilted relative to a longitudinal axis of the pistons to vary adisplacement of the pistons within their respective bores. Althoughshown in FIG. 2 as producing only a unidirectional flow of pressurizedfluid, it is contemplated that pump 28 may alternatively be anover-center pump or rotatable in opposing directions to produce flows offluid in two directions, if desired.

When swashplate 40 rotates relative to the pistons, the angled drivingsurface of swashplate 40 may drive each piston through a reciprocatingmotion within each bore. When the piston is retracting from the bore,fluid may be allowed to enter the bore from inlet passage 30. When thepiston is moving into the associated bore under the force of the drivingsurface of swashplate 40, the piston may force the fluid at an elevatedpressure from the bore toward systems 14, 16 via outlet passage 32. Theangular setting of swashplate 40 relative to the pistons may affect adischarge rate of the pressurized fluid and be adjustable bydisplacement actuator 34.

Displacement actuator 34 may include components that function to adjustthe tilt angle of swashplate 40 and subsequently the effectivedisplacement volume of each piston/bore paring of pump 28. Specifically,displacement actuator 34 may include one or more control pistons 42 thatdirectly or indirectly press against a portion of swashplate 40 to urgeswashplate 40 to tilt relative to the axial direction of the pump'spistons. In the disclosed embodiment, control piston 42 is a dual-actingpiston that is movable in response to a force imbalance caused by fluidpressure acting on opposing sides of a piston member. In particular,control piston 42 may be continuously connected at one end (e.g., at arod-end) 44 to outlet passage 32 via a first actuator passage 46, andselectively connected at an opposing end (e.g., at a head-end) 48 tooutlet passage 32 via a second actuator passage 50. The connectionlocation of second actuator passage 50 to outlet passage 32 may bedownstream of the connection location of first actuator passage 46. Whenfluid of a sufficient pressure is introduced into end 48 of displacementactuator 34, displacement actuator 34 may be caused to move swashplate40 from a maximum displacement position toward a minimum displacementposition by an amount and/or at a rate corresponding to the forceimbalance across the piston member of displacement actuator 34. It iscontemplated that displacement actuator 34 may alternatively include aspring-biased single-acting piston, if desired.

Displacement control valve 36 may be associated with displacementactuator 34 to control a flow of fluid from outlet passage 32 throughsecond actuator passage 50 into second end 48, thereby controlling inwhich direction (i.e., which of a displacement-increasing and adisplacement-decreasing direction) swashplate 40 of pump 28 is moved bydisplacement actuator 34. Displacement control valve 36 may be aspring-biased, electro-hydraulic control valve that is movable based ona command from controller 38. In particular, displacement control valve36 may include a first valve element 52 that is pilot-operated tocontrol fluid flows to and from displacement actuator 34, and a secondvalve element 54 that is solenoid-operated to control movement of firstvalve element 52 when energized by controller 38

First valve element 52 may be movable between a first position at whichsecond end 48 of displacement actuator 34 receives pressurized fluid viasecond actuator passage 50, and a second position (shown in FIG. 2) atwhich fluid flow through second actuator passage 50 into second end 48is blocked and second end 48 is instead connected to tank 26. A firstpilot passage 56 may direct pilot fluid from outlet passage 32 to afirst end 58 of first valve element 52 to urge first valve element 52toward the first position, and a second pilot passage 60 may directpilot fluid from outlet passage 32 to a second end 62 of first valveelement 52 to urge first valve element 52 toward the second position.First pilot passage 56 may connect to outlet passage 32 at a locationupstream of the connection locations of second actuator passage 50 andsecond pilot passage 60 with outlet passage 32, and downstream of theconnection location of first actuator passage 46 with outlet passage 32.Second pilot passage 60 may connect to outlet passage 32 at a connectionlocation downstream of second actuator passage 50 and upstream ofsystems 14, 16. First valve element 52 may be spring-biased toward thesecond position. A restricted orifice 64 may be placed within secondpilot passage 60 to create a pressure drop that facilitates control offirst valve element 52.

Second valve element 54 may be movable from a first position at whichsecond pilot passage 60 is pressurized by fluid from outlet passage 32,toward a second position at which second pilot passage 60 is fluidlyconnected to tank 26. Second valve element 54 may be selectivelyenergized by controller 38 to move toward the second position, andspring-biased toward the first position. When second valve element 54 isin the second position and second pilot passage 60 is fluidly connectedto tank 26, a pressure drop may be generated across restricted orifice64 (i.e., a pressure within second pilot passage 60 between restrictedorifice 64 and first valve element 52 may be reduced) that allows thepressurized fluid within first pilot passage 56 to move first valveelement 52 toward the second position. Second valve element 54 may beinfinitely variable, and movable to any position between its first andsecond positions, thereby affecting a corresponding variable movement offirst element 54 between its first and second position and,subsequently, a movement of displacement actuator 34. It should be notedthat the magnitude of the electrical current passing through thesolenoid of second valve element 54 may correspond with the positionachieved by second valve element 54. In other words, a particularcurrent may be selectively applied to second valve element 54 bycontroller 38 to cause second valve element 54 to move to a desiredposition that results in movement of first valve element 52 also to adesired position and a corresponding desired velocity of displacementactuator 34 and tilt angle of swashplate 40.

One or more pressure relief or pressure limiting valves 66 may also befluidly communicated with second pilot passage 60. Pressure relief valve66 may be spring-biased and movable in response to a pressure of secondpilot passage 60 to selectively connect second pilot passage 60 withtank 26, thereby relieving or limiting excessive fluid pressures.

Controller 38 may embody a single or multiple microprocessors, fieldprogrammable gate arrays (FPGAs), digital signal processors (DSPs), etc.that include a means for controlling an operation of pump system 24.Numerous commercially available microprocessors can be configured toperform the functions of controller 38. It should be appreciated thatcontroller 38 could readily embody a microprocessor separate from thatcontrolling other machine-related functions, or that controller 38 couldbe integral with a machine microprocessor and be capable of controllingnumerous machine functions and modes of operation. If separate from thegeneral machine microprocessor, controller 38 may communicate with thegeneral machine microprocessor via datalinks or other methods. Variousother known circuits may be associated with controller 38, includingpower supply circuitry, signal-conditioning circuitry, actuator drivercircuitry (i.e., circuitry powering solenoids, motors, or piezoactuators), and communication circuitry.

Controller 38 may be in communication with second valve element 54 viaan electrical circuit 68, and be configured to energize second valveelement 54 by selectively directing an electrical current throughcircuit 68. The amount of current directed through circuit 68 bycontroller 38 may correspond with a desired amount of torque that shouldbe absorbed by pump 28 (i.e., with a torque limit of pump 28), andresult in a specific change in the tilt angle of swashplate 40. Thedesired amount of torque may be determined based on operating conditionsof engine 20, as is known in the art, such that engine stall does notoccur and engine 20 functions in an efficient manner. Because thesolenoid of second valve element 54 may be a relativelyconstant-resistance device, controller 38 may vary the current passingthrough circuit 68 and thereby regulate motion of second valve element54 (and the subsequent motion of swashplate 40), by adjusting a voltageapplied to circuit 68.

As is known in the art, an amount of torque absorbed by a pump isproportional to a product of the pump's displacement and a pressure offluid discharged from the pump (i.e., Torque≈Displacement×Pressure).Accordingly, when controller 38 adjusts a voltage applied to secondvalve element 54 and the angle of swashplate 40 responsively changes,the amount of torque absorbed by pump 28 should likewise change in animmediate step-wise manner. However, this step-wise change indisplacement may also have a longer term effect on the pressure of pumpsystem 24, as the displacement change may cause fluid to be dischargedinto pump system 24 at a faster or slower rate (depending on thedisplacement change direction). The rising or lowering of systempressure, if left unchecked, could cause an actual torque absorption ofpump 28 to deviate away from the desired torque absorption amount afterthe change in swashplate angle has been implemented. In conventionalsystems, sensory feedback is required to provide information regardingdisplacement position and/or discharge pressure to help ensure that thedesired amount of torque is being absorbed. In the disclosed system,however, a desired torque absorption of pump 28 may be maintainedwithout the use of any such sensors. Instead of additional sensors, pumpsystem 24 may include a variable resistor 67 that functions to adjust atotal resistance of circuit 68 as swashplate 40 moves, thereby varyingthe amount of current passing through the solenoid of second valveelement 54.

In the disclosed embodiment, variable resistor 67 may be anelectro-mechanical device having a sliding contact (not shown), alsoknown as a wiper, that functions as an adjustable voltage divider. Thewiper may be mechanically connected to one or both of displacementactuator 34 or swashplate 40, and be configured to vary a resistance ofcircuit 68 during displacement-adjusting movements of the associatedcomponent(s). In other words, as displacement actuator 34 and/orswashplate 40 moves to adjust a displacement of pump 28 in response to avoltage change implemented by controller 38, the wiper of variableresistor 67 may also simultaneously move to adjust a resistance ofcircuit 68. This adjustment of the resistance of circuit 68, for a givenapplied voltage, may result in a change in the current passing throughsecond valve element 54 and the torque absorption of pump 28.Accordingly, variable resistor 67 may function as a feedback mechanismfor pump system 24 such that a desired torque absorption level of pump28 may be maintained, even as the pressure of system 24 changes as aresult of a swashplate angle change.

A signal conditioning device 74 may be connected to circuit 68 andconfigured to condition the current passing through the solenoid ofsecond valve element 54, if desired. Although shown as being locatedbetween variable resistor 67 and the solenoid of second valve element54, it is contemplated that signal conditioning device 74 could bepositioned at any other location along circuit 68, such as betweencontroller 38 and second valve element 54 or between variable resistor67 and a ground 76, as desired. Signal conditioning device 74 mayinclude, for example, additional resistors, capacitors, amplifiers, andother known electronic components.

FIG. 3 illustrates another embodiment of pump system 24. Similar to pumpsystem 24 of FIG. 2, pump system 24 of FIG. 3 includes tank 26, pump 28,displacement control valve 36, and controller 38. However, pump system24 of FIG. 3 may be a load-sense type of system. That is, the connectionof second actuator passage 50 with outlet passage 32 may be locatedbetween a valve stack 70 (i.e., a stack of one or more control valves)and a working actuator 72 of tool and/or drive systems 14, 16. In thismanner, a load on working actuator 72 may be sensed and used to helpcontrol the motion of first valve element 52.

INDUSTRIAL APPLICABILITY

The disclosed pump system may be applicable to any machine where precisecontrol over torque absorption in a simplified manner is desired. Thedisclosed pump system may provide for precise control of torqueabsorption by utilizing a variable resistor to vary current directedthrough a displacement control valve based on changing pumpdisplacement. The disclosed system may be simple, as no sensor or costlyfeedback control loops are required. Operation of pump system 24 willnow be described.

During operation, engine 20 may drive pump 28 to rotate and pressurizefluid. The pressurized fluid may be discharged from pump 28 into outletpassage 32 and directed into working actuators 72 of tool and/or drivesystems 14, 16. As the pressurized fluid passes through workingactuators 72, hydraulic power in the fluid may be converted tomechanical power used to move machine 10.

The fluid discharge direction and displacement of pump 28 may beregulated, at least in part, based on a desired torque absorptionamount. Controller 38 may determine the desired torque absorption amountin a conventional manner, and then generate an open-loop torque commandthat results in application of a corresponding voltage to the solenoidof second valve element 54. Second valve element 54, in response to theapplied voltage, may move to a particular position between its first(i.e., flow-blocking) position and its second (i.e., flow-passingposition), thereby moving first valve element 52 to a particularposition between its first and second position. The movement of firstvalve element 52 to the particular position may result in a desiredforce imbalance across the piston member of displacement actuator 34that functions to change a tilt angle of swashplate 40 and resultingdisplacement of pump 28. This displacement change, in conjunction withthe instantaneous pressure of pump system 24, may cause pump 28 toabsorb the desired amount of torque.

After the displacement of pump 28 has been changed, however, thepressure within pump system 24 may gradually change (i.e., increase ordecrease based on the displacement change direction). This changingpressure, if left unaccounted, may cause the actual torque absorption ofpump 28 to deviate from the desired torque absorption amount.Accordingly, as the displacement of pump 28 changes, variable resistor67 may adjust the resistance of circuit 68. This adjustment to theresistance of circuit 68 may function to change the current flowingthrough the solenoid of second valve element 54, thereby varying thetilt angle of swashplate 40 such that a relatively constant torqueabsorption of pump 28 may be maintained.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed pump system.Other embodiments will be apparent to those skilled in the art fromconsideration of the specification and practice of the disclosed pumpsystem. It is intended that the specification and examples be consideredas exemplary only, with a true scope being indicated by the followingclaims and their equivalents.

1. A pump system, comprising: a pump having a displacement that isvariable; an actuator movable to adjust the displacement of the pump; anelectro-hydraulic valve fluidly connected to the actuator and configuredto control movement of the actuator; and a variable resistormechanically connected to at least one of the actuator and the pump, andbeing adjustable by movement of the at least one of the actuator and thepump to vary a current passing through the electro-hydraulic valve. 2.The pump system of claim 1, wherein the actuator is fluidly connected ata first end to an output of the pump and at an opposing second end tothe electro-hydraulic valve.
 3. The pump system of claim 2, wherein theelectro-hydraulic valve includes: a pilot-operated valve element movablefrom a first position at which the second end of the actuator is fluidlyconnected to the output of the pump, and a second position at which thesecond end of the actuator is fluidly connected to a low-pressure tank;and a solenoid-operated valve element operable to control movement ofthe pilot-operated valve element between the first and second positions.4. The pump system of claim 3, further including: at least one workingactuator; an outlet passage extending from the pump to the at least oneworking actuator; a control valve disposed within the outlet passage andconfigured to regulate operation of the at least one working actuator; afirst pilot passage extending from the outlet passage, at a firstlocation upstream of the control valve, to a first end of thepilot-operated valve element; a second pilot passage extending from theoutlet passage, at a second location upstream of the control valve anddownstream of the first location, to a second end of the pilot-operatedvalve element; and a restricted orifice disposed within the second pilotpassage.
 5. The pump system of claim 4, wherein the solenoid-operatedvalve element is configured to selectively relieve pressure in thesecond pilot passage by an amount corresponding to current passingthrough the electro-hydraulic valve.
 6. The pump system of claim 5,wherein the pilot-operated valve element is spring-biased toward thesecond position.
 7. The pump system of claim 6, further including atleast one of pressure relief or pressure limiting device fluidlyconnected to the second end of the pilot-operated valve element.
 8. Thepump system of claim 1, further including a signal conditioning devicelocated between the variable resistor and the electro-hydraulic valve.9. The pump system of claim 1, further including a controller incommunication with the electro-hydraulic valve and configured to issuean open-loop torque command to the electro-hydraulic valve.
 10. The pumpof claim 3, further including: at least one working actuator; an outletpassage extending from the pump to the at least one working actuator; acontrol valve disposed within the outlet passage and configured toregulate operation of the at least one working actuator; a first pilotpassage extending from the outlet passage, at a first location upstreamof the control valve, to a first end of the pilot-operated valveelement; a second pilot passage extending from the outlet passage, at asecond location between the control valve and the at least one workingactuator, to a second end of the pilot-operated valve element; and arestricted orifice disposed within the second pilot passage.
 11. A pumpsystem comprising: a pump having a displacement that is variable; atleast one working actuator configured to receive pressurized fluid fromthe pump; an outlet passage extending from the pump to the at least oneworking actuator; a control valve disposed within the outlet passage andconfigured to regulate operation of the at least one working actuator; apump actuator movable to adjust the displacement of the pump, and beingfluidly connected at a first end to the outlet passage; a pilot-operatedvalve element movable from a first position at which a second end of thepump actuator is fluidly connected to the outlet passage, and a secondposition at which the second end of the pump actuator is fluidlyconnected to a low-pressure tank; a first pilot passage extending fromthe outlet passage, at a first location upstream of the control valve,to a first end of the pilot-operated valve element; a second pilotpassage extending from the outlet passage, at a second location upstreamof the control valve and downstream of the first location, to a secondend of the pilot-operated valve element; a spring configured to bias thepilot-operated valve element toward the second position; a restrictedorifice disposed within the second pilot passage; a solenoid-operatedvalve element operable to control movement of the pilot-operated valveelement between the first and second positions; a variable resistormechanically connected to at least one of the actuator and the pump andbeing adjustable by movement of the at least one of the actuator and thepump to vary a current passing through the solenoid-operated valveelement; and a controller in communication with the solenoid-operatedvalve element and configured to issue an open-loop torque command to thesolenoid-operated valve element.
 12. A method of controlling a pump,comprising: operating the pump to pressurize a fluid; generating anelectronic signal indicative to adjust a displacement of the pump; andhydro-mechanically adjusting the displacement of the pump based on thesignal, wherein hydro-mechanically adjusting the displacement the pumpalso simultaneously modifies a resistance of the electronic signal. 13.The method of claim 12, wherein hydro-mechanically adjusting thedisplacement of the pump includes continuously connecting a pump outletpressure with a first end of a pump actuator, and selectively connectinga second end of the pump actuator to the pump outlet pressure or alow-pressure tank.
 14. The method of claim 13, wherein selectivelyconnecting a second end of the pump actuator to the pump outlet pressureor a low-pressure tank includes directing the electronic signal to movea first valve element that hydraulically biases a second valve elementbetween a first position and a second position.
 15. The method of claim14, further including: directing pressurized fluid from the pump througha control valve to a working actuator; directing first and second flowsof pressurized pilot fluid from upstream of the control valve to firstand second ends of the second valve element, respectively; andrestricting the second flow of pressurized pilot fluid, wherein movementof the first valve element results in a least a portion of the secondflow of pressurized pilot fluid being directed to the low-pressure tankto reduce a pressure of the second flow of pressurized pilot fluid. 16.The method of claim 15, wherein an amount of the second flow ofpressurized pilot fluid directed to the low-pressure tank correspondswith an amount of current in the electronic signal passing to the firstvalve element.
 17. The method of claim 16, further includingmechanically biasing the second valve element toward the secondposition.
 18. The method of claim 17, further including relieving apressure of the second flow of pressurized pilot fluid when a pressureof the second flow of pressurized pilot fluid exceeds a thresholdpressure.
 19. The method of claim 14, further including: directingpressurized fluid from the pump through a control valve to a workingactuator; directing a first flow of pressurized pilot fluid fromupstream of the control valve to a first and end of the second valveelement; directing a second flow of pressurized pilot fluid fromdownstream of the control valve and upstream of the working actuator toa second end of the second valve element; and restricting the secondflow of pressurized pilot fluid, wherein movement of the first valveelement results in a least a portion of the second flow of pressurizedpilot fluid being directed to the low-pressure tank to reduce a pressureof the second flow of pressurized pilot fluid.
 20. The method of claim12, wherein generating an electronic signal includes generating anopen-loop torque command.